2. Astronomy

3. Chapter Nineteen: Galaxies and the Universe 19.1 Tools of Astronomers 19.2 Stars 19.3 Galaxies and the Universe

4. Investigation 19A How does a telescope work? Tools of Astronomy

5. 19.1 Tools of Astronomers An astronomer is a scientist who studies objects in space. The universe is defined as everything that exists, including all matter and energy.

6. 19.1 Writing very large numbers Scientific notation is a mathematical abbreviation for writing very large (or very small) numbers. How do scientists write the number 150,000,000?

8. 19.1 Units of distance in space Astronomers have developed units other than kilometers or meters to measure the vast distances in space. One light year is equal to the distance that light travels through space in one year.

9. 19.1 Studying the universe A galaxy is a huge collection of gas, dust, and billions of stars. Our galaxy, the Milky Way, contains billions of stars!

10. 19.1 Studying the universe Light from other galaxies and stars takes time to reach Earth. The farther away the object they are viewing, the further back in time astronomers are looking.

11. 19.1 Telescopes A telescope is a device that makes objects that are far away appear closer. In the 1600s, Galileo was the first to use a telescope for viewing the night sky.

12. 19.1 Telescopes Telescopes work by collecting the light from a distant object with a lens or mirror and bringing that light into a concentrated point, called the focal point.

13. 19.1 Telescopes A refracting telescope uses lenses to bend, or refract, light, making objects look bigger. Refracting telescopes are made from a long tube, a glass objective lens that you point toward the sky, and an eyepiece lens.

14. 19.1 Telescopes A reflecting telescope uses mirrors instead of lenses to gather and focus light. A concave mirror (called the primary mirror) is placed at the back of a tube. The secondary mirror deflects the light to an eyepiece lens.

15. 19.1 Other types of telescopes Astronomers use different types of telescopes to view the different types of waves emitted by objects in space. 1.A radio telescope works like an extremely powerful receiver that picks up radio waves from space. 2.In 1983, the Infrared Astronomical Satellite (IRAS) was launched to map the entire sky at infrared wavelengths. 3.X-ray telescopes are designed to detect high-energy radiation (X-rays) from space.

16. 19.1 Other types of telescopes These three images of the Crab Nebula were taken with different telescopes. Each new view gives astronomers more information.